Flow diverter

ABSTRACT

A flow diverter for connecting a central bore to an outer conduit. The flow diverter defines a portion of the central bore and angled flow passages connecting the portion of the central bore to the outer conduit. Rounded edges between the central bore and angled flow passages reduce cavitation and/or turbulence. The rounded edges and an adjacent portion of the central bore may be defined by an insert. The insert may define walls extending fully around portions of the angled flow passages.

PRIORITY CLAIM

This application claims priority from Canadian Patent Application No.3020846 filed Oct. 15, 2018, which is a continuation of U.S. patentapplication Ser. No. 16/653,949 filed Oct. 15, 2019, which is acontinuation-in-part of U.S. patent application Ser. No. 15/808,843filed Nov. 9, 2017 (now U.S. Patent No. 10900304), which claims priorityfrom Canadian Patent Application No. 2982295 filed Oct. 13, 2017, whichapplications are incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

Flow diverter.

BACKGROUND OF THE INVENTION

A “flow diverter” refers to an element shaped to define one or more flowchannels connecting a typically annular first conduit with a secondconduit. One example context in which a flow diverter is used is in adrilling motor for powering a drill bit. Drilling mud flows through abore to a power section of a drilling motor to power the drilling motor.The mud then flows through an annular conduit around a coupling betweenthe power section and a bearing section. The flow is from power sectionto transmission (including drive shaft/cv joint) to bearing section andout the drill bit. The flow diverter connects the transmission to thebearing section. The annular conduit continues around an upper end ofthe bearing section. The bearing section has a central bore throughwhich mud flows to lubricate the drill bit. The mud flows from theannular conduit to the central bore via a flow diverter having angledports connecting the annular conduit to the bore. As the flow diverteris connected to the bearing section it is rotating with the bearingsection at typically between 100-250 rpm. In some cases, there may be aflow diverter before the transmission on the upper end of a drive shaftin the transmission section for mud motors that can relieve pressurethrough a central bore in the power section's rotor. In this case theflow diverter would be connected at the flow channel end to thetransmission of a drilling motor and at the bore end to a thru borepower section rotor. The flow direction would be reversed, with the flowcoming through the bore and out the flow channels. However, theinvention as claimed would serve in that location as well. Thus, a flowdiverter handles mud flow around the transmission (drive shaft, cvjoints) returning it to a central bore through the bearing section.Conventional flow diverter designs can have various angles of the portsrelative to the bore, for example at 90 degrees, 45 degrees, or 30degrees. The mud flow can be for example 200-600 gpm and there aretypically 4 ports of diameter about 1″. This flow of mud through theangled ports into the bore can result in washout in the walls of thediverter at or near the intersection of the bore and the ports. Thediverter is typically scrapped when the walls are deemed compromised dueto a certain amount of washout being present. These parameters are for6½″ motor parts, which is the size used in the flow simulations in thisdocument. Different sized parts will result in different figures.

The example figures given above lead to an average flow speed of mud ofabout 20 to 60 ft/s through the 4 ports. According to SchlumbergerOilfield Glossary, “For erosion to occur usually requires a high fluidvelocity, on the order of hundreds of feet per second, and some solidscontent, especially sand.” The bore of a flow diverter may have asmaller total area than the ports, depending on the pressure and flowrequired by the mod motor or turbine. This can lead to a higher averageflow speed in the bore than in the ports, but the speeds will typicallyremain below the hundreds of feet per second stated by Schlumberger tobe needed for erosion. A person skilled in the art might thereforeconclude that flow diverters should not wash out. Nonetheless, washoutof the bore is observed to occur near the ports.

Due to the positioning of the washout near the ports, a cylindrical wearsleeve may not adequately protect a flow diverter from washout, and inany case might have to be replaced frequently due to the above mentionedwashout occurring to the wear sleeve, with corresponding inconvenienceand expense. Thus, there is a need for improved lifespan of flowdiverters.

SUMMARY OF THE INVENTION

There is provided a flow diverter having bore walls defining a bore andinlet walls defining a flow channel acting as an inlet to the bore inuse in the downhole drilling motor. The flow diverter is configured todirect an inlet fluid flow at an inlet flow rate into the bore via theflow channel and to direct a downstream flow at a downstream flow ratein a downstream direction within the bore downstream of the inlet.Transitional wall portions form a transition between the inlet walls andthe bore walls at least in the downstream direction from the flowchannel. The transitional wall portions are configured to besufficiently smooth and to have sufficient radius of curvature toprevent cavitation within the bore at the transitional wall portions andimmediately downstream of the transitional wall portions when fluidflows at the inlet flow rate into the bore via the flow channel and atthe downstream flow rate in the downstream direction within the boredownstream of the flow channel. This can also be done with a reversedflow direction, in which case the parameters are chosen to preventcavitation within the flow channel, which is downstream of the change indirection in this case.

In various embodiments, there may be included any one or more of thefollowing features: the radius of curvature may be greater than onethird of a diameter of the flow channel. The radius of curvature may begreater than one half of a diameter of the flow channel. The radius ofcurvature may be greater than three quarters of a diameter of the flowchannel. The flow diverter may comprise a housing and an insert, theinsert comprising the transitional wall portions, and the housingcomprising the inlet walls or the bore walls. The insert may comprisethe transitional wall portions and at least a portion of the bore wallsdownstream of the inlet, and the housing may comprise the inlet walls.The housing may comprise the inlet walls and the bore walls. The flowdiverter may comprises a housing and an insert, the insert comprisingthe transitional wall portions and defining portions of the inlet wallsextending fully around the flow channel. The flow channel may be one ofplural flow channels defined by additional inlet walls, the inlet wallsand the additional inlet walls converging to a point upstream of thebore to form a pyramid-shaped tip. A cross section of the pyramid-shapedtip parallel to the flow direction may have a concave profile. Thesefeatures of the pyramid-shaped tip may also be present in the flowdiverter even where there is no insert (although this would make itharder to manufacture). The flow channel may extends between the boreand an exterior surface of a tubular, the tubular having a firstdiameter at an upstream end of the tubular larger than a second diameterof the tubular at the flow channel, the tubular defining a transitionarea between the first diameter and the second diameter, the transitionarea having a slope of 45 degrees or less.

There is also provided a flow diverter having a body defining a centralbore. The central bore has an opening at a first end of the body, andthe body further defines flow channels angled relative to the centralbore and connecting the central bore to an exterior surface of the body.The body also defines fillets connecting the flow channels to thecentral bore and having a radius of curvature greater than one third ofa diameter of a flow channel of the flow channels.

In various embodiments, there may be included any one or more of thefollowing features: the radius of curvature may be greater than one halfof a diameter of the flow channel. The radius of curvature may begreater than three quarters of a diameter of the flow channel. the bodymay comprise a housing defining a cavity extending from the opening andan insert inserted within the cavity, the insert defining the fillets.The housing may be formed of a first material and the insert may beformed of a second material more abrasion resistant than the firstmaterial. There may be a first connector at the first end configured toconnect the flow diverter to a bearing section of a drilling motor and asecond connector at a second end opposite to the first end configured toconnect the flow diverter to a coupling for connecting to a transmissionof the drilling motor. There may be a first connector at the first endconfigured to connect the flow diverter to a transmission of a drillingmotor and a second connector at a second end opposite to the first endconfigured to connect the flow diverter to a coupling for connecting toa through bore power section rotor of the drilling motor.

There is also provided an insert for a flow diverter, the insertdefining a central bore and having curved portions adjacent to thecentral bore configured to, when the insert is inserted in the flowdiverter, form fillets connecting the central bore to flow channelsdefined by the flow diverter, the flow channels being angled relative tothe central bore and connecting the central bore to an exterior surfaceof the flow diverter when the insert is inserted in the flow diverter.

In various embodiments, there may be included any one or more of thefollowing features: the insert may also have inlet wall portionsextending fully around each of the flow channels. The inlet wallportions may converge to a point upstream of the central bore to form apyramid-shaped tip. A cross section of the pyramid-shaped tip parallelto the flow direction may have a concave profile.

These and other aspects of the device are set out in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred and alternative examples of the present invention aredescribed in detail below with reference to the following drawings:

FIG. 1 is a side cutaway of a flow diverter;

FIG. 2A is an end view of an insert in the flow diverter of FIG. 1;

FIG. 2B is a side cutaway of the insert of FIG. 2A as cut on sectionlines B-B as shown in FIG. 2A, and is also a closeup of the insert asshown in FIG. 1;

FIG. 3 is an isometric view of the flow diverter of FIG. 1;

FIG. 4 is a cutaway exploded isometric view of the flow diverter of FIG.1, with a dashed line showing a central axis along which the insert isdisplaced out of the flow diverter;

FIG. 5 is a side section view of a prior art flow diverter having a longand thin outlet;

FIG. 6 is a side section view of a modified version of the flow diverterof FIG. 5 including an access opening from an upstream direction, and aninsert that plugs the access opening in installed position;

FIG. 7 is a cutaway exploded isometric view of the flow diverter andinsert of FIG. 6;

FIG. 8 is a closeup side section view of the insert for the modifiedflow diverter of FIG. 6;

FIG. 9 is a side section view of another prior art flow diverter;

FIG. 10 is a side section view of a modified version of the flowdiverter of FIG. 9 including an insert defining full portions of inletchannels;

FIG. 11 is a cutaway exploded isometric view of the flow diverter andinsert of FIG. 10;

FIG. 12 is a closeup side section view of the insert for the modifiedflow diverter of FIG. 10,

FIG. 13 is a side section view of another prior art flow diverter.

FIG. 14 is a side section view of a housing of a modified flow diverterbased on the flow diverter of FIG. 13 showing a widening of the bore toreceive an insert;

FIG. 15 is a side section view of the modified flow diverter of FIG. 14including the insert;

FIG. 16 is another modified flow diverter based on the flow diverter ofFIG. 13, this one including an insert as shown in FIG. 12;

FIG. 17 is a frame of a simulation showing flow in a closeup of a priorart flow diverter;

FIG. 18 is a frame of a simulation showing flow in a closeup of amodified flow diverter having rounded connections between flow channelsand bore and with a void behind the intersection of the flow channelsand bore filled in;

FIG. 19 is a frame of a simulation showing flow and cavitation areas ina frame of a simulation of a prior art flow diverter;

FIG. 20 is a frame of a simulation showing flow and low pressure areasin a frame of a simulation of a modified flow diverter having roundedconnections between flow channels and bore but still having a voidbehind the intersection of the flow channels and bore.

FIG. 21 is an initial frame of a simulation showing flow and cavitationareas in a modified flow diverter having rounded connections betweenflow channels and bore and with a void behind the intersection of theflow channels and bore filled in, the cavitation areas appearing in thisinitial frame but quickly disappearing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The inventors believe that washout occurs in conventional flow divertersand other fluid handling mechanisms due to the turbulence and(hydrodynamic) cavitation caused as the fluid traverses an angle betweenthe straight flow channel and straight bore. As fluid traverses a sharpangle where a wall diverges away from the incoming flow direction, ithas momentum carrying it in its original direction resulting in a sharppressure drop adjacent to the wall downstream of the angle. Thispressure drop may be enhanced where the downstream wall is a boundary ofa constricted channel where Bernoulli's principle applies, but thelocalized pressure immediately downstream of the angle at the wall maybe well below the pressure expected from Bernoulli's principle given theaverage flow rate. The localized pressure drop can lead to cavitation atthe wall shortly downstream of the angle. Due at least to turbulence,the cavitation is not steady but may repeatedly collapse leading todamage to the walls. Cavitation bubbles may also continue downstream andcollapse leading to damage shortly downstream of the angle. Typically,there is additional equipment downstream of the flow diverter with thesame central bore configuration, which will also benefit from the flowdiverter embodiments disclosed here. Washout will occur in other fluidhandling devices for the same reasons and thus the solution proposedbelow may also be applied to other applications where a wall divergesaway from an incoming flow direction.

In order to reduce this disturbed fluid flow, there are thereforeprovided curved transition surfaces between the angled flow channels andthe bore. The curved surfaces alter the flow at the exit point of theangled flow port or ports into the bore, creating a smoothed transitioninto the bore. The fluid traverses the angle gradually reducing theabrupt pressure drop at the walls present in a sharp transition. Theyalso lower the fluid velocity creating a more gradual change in velocityand pressure at and beyond the transition. For the purpose of thisdocument, these curved surfaces shaped to reduce cavitation and/orturbulence will be referred to as fillets. However, fabricating thefillets may pose challenges if the flow diverter is formed as one piece.For example, forming the fillets by machining would be difficult if notimpossible in a one piece configuration. Thus, in an embodiment aninsert is provided defining the fillets. The insert may also act as awear sleeve which defines the bore at the intersection of the bore andflow channels, and immediately downstream of the intersection. An insertmay also be inserted in an inlet flow channel and may define walls ofthe inlet flow channel and the fillet corresponding to the inlet flowchannel. The insert may be made of a different material than the rest ofthe flow diverter. Thus the insert can be made out of various materialsto provide the best possible wear resistance and part life for theconditions it is being used in. For example the insert may be made of amore abrasion resistant material to increase washout resistance.However, testing is showing that the same material as the housing isperforming well with only the geometry modifications. The insert mayalso have various surface treatments including coatings and treatmentsthat alter the surface texture to modify boundary layer conditionsand/or the fluid interaction with the surface of the sleeve.

The fillets may have an elliptical profile as seen in a cross sectionperpendicular to the flow. The fillets may have a radius that isvariable based on the entry angle of the port. In the example shown inFIG. 10, dashed circle 80 with dotted radius line 82 represents theradius of curvature of a fillet 20 as seen in a cross section parallelto the flow. As can be seen in FIG. 10, the radius of curvature in thiscase is slightly less than a diameter 84 of the flow channels 44. Forexample, the radius of curvature 82 may in different embodiments begreater than ⅓, ½, or ¾ of the diameter 84. It could also be larger thanthe diameter 84. A profile need not correspond exactly to a portion of acircle to have a radius of curvature. Parameters of the profile may bechosen to mitigate cavitation.

An exemplary embodiment is described in relation to FIGS. 1-4.

FIG. 1 shows a side cross section of the exemplary embodiment of theflow diverter. As shown in FIG. 1, the flow diverter 10 comprises a bodyformed of a housing 12 and an insert 14. The body defines a central bore16, a portion of the central bore being defined by insert 14, and thehousing defines angled flow channels 44 connecting the central bore toan outer surface 18 of the housing. The insert defines curved surfaces20 which form fillets in relation to the central bore and angled flowchannels. The bore has an open end 22 and a closed end 24. The filletsconnect to portions 26 of the angled flow channels positioned in adirection of intended flow from the angled flow channels into the bore,or if flow in the opposite direction occurred, positioned in a directionfrom which flow occurs from the bore into the angled flow channels. Theportions 26 will thus be outer portions of the angled flow channelswhere the angled flow channels are at less than 90 degrees with respectto the bore, or portions closer to the open end of the bore where thereis an open end and a closed end. In this embodiment, no fillets arepresent at opposite edges 28 which are away from the intended directionof flow from the angled flow channels into the bore. At the open end 22there is a coupling 30 for coupling the flow diverter to a bearingsection of a drilling motor. At the closed end 24 there is a coupling 32for coupling the flow diverter to a coupling for connecting to atransmission of the drilling motor.

FIG. 2a and FIG. 2B show the insert 14 more closely. FIG. 2A is an endview and FIG. 2B is a side cutaway view of the insert 14 showing fillets20 and end portions 34 which contact the housing between the angled flowchannels. In the embodiment shown, the fillets curve smoothly from thecentral bore 16 to portions 36 which are aligned with cylindrical wallsof the angled flow channels when the insert is inserted into thehousing.

FIG. 3 shows an isometric view of the flow diverter showing coupling 32at closed end 24. The housing has a narrower portion 38 at closed end 24and a wider portion 40 at open end 22. The outer surface of the housingat narrower portion 38 defines an inner boundary of an annular channelto which the angled flow channels 44 connect when the flow diverter isinstalled in a drilling motor.

FIG. 4 shows a cutaway exploded isometric view of the flow diverter ofFIG. 1. The insert 14 is shown displaced out of the flow diverter in thedirection of the open end 22. Dashed line 42 shows a central axis alongwhich the insert is displaced in this example.

FIG. 5 shows a prior art flow diverter design. The open end coupling 30for this flow diverter is a male connector, resulting in the portion ofthe central bore 16 downstream of the angled flow channels 44 being toolong and narrow for it to be practical to modify the prior art diverterdesign to include an insert of the design disclosed in FIGS. 1-4. Also,in this diverter, the upstream end of the housing 12 is wider. The outersurface 18 of the housing 12 defines the inner boundary of an annularchannel, including at the wider upstream end. Flow proceeds along thisannular channel from left to right in this figure, until the flowreaches the angled flow channels 44. Beyond this point the annularchannel continues but may be stagnant or reversing, as the flow isdiverted to the central bore 16. As with all flow diverter designs shownin this document, in normal operation flow proceeds from the outerdiameter 18, through the angled flow channels 44 and out the centralbore 16.

FIG. 6 shows a modification of the prior art flow diverter design ofFIG. 5 to include another embodiment of an insert 14. In this flowdiverter embodiment, the insert 14 is inserted from the upstream(“closed”) end 24 of the central bore 16. This insert defines walls 46extending fully around, thus defining a portion of the length of, eachof the angled flow channels 44. In some cases there is a sealed ConstantVelocity drive joint (not shown in this figure, but shown in FIGS.13-16) in place of an API threaded connection as the closed endconnector 32. To prevent the joint from being exposed to the fluidpressure, the insert has a closed end portion 48 that acts to plug thecentral bore 16 to define the closed end of the central bore. Where sucha fluid connection is not a concern, the closed end portion 48 could beomitted or include a hole (not shown). The shape of the closed endportion 48 as shown provides further benefits that will be describedbelow in relation to FIGS. 10-12.

FIG. 7 is a cutaway exploded isometric view of the flow diverter andinsert of FIG. 6. The insert 14 in this embodiment is inserted into thehousing 12 from the upstream end through coupling 32 to the transmissionand comes to rest at seat 50.

FIG. 8 is a closeup side section view of the insert for the modifiedflow diverter of FIG. 6. The walls 46 defining the portion of the flowchannels in the insert connect an open end portion 52 of the insert,defining curved surfaces 20, to the closed end portion 48.

FIG. 9 shows another prior art flow diverter. This diverter, as with theflow diverter of FIGS. 1-4, has a wide open end 22 of the bore 16 andcan be modified to have an insert inserted from the open (downstream)end 22 and no plug is needed. This flow diverter could thus be modifiedto have an insert as shown in FIG. 1. However, in FIG. 10 a modifiedflow diverter is shown that has an insert 14 inserted from the right anda closed end portion 48.

The prior art flow diverter of FIG. 9 has no insert and is formed bymachining the central bore 16 from the open end 22 beyond where theangled flow channels 44 will intersect, and drilling angled flowchannels 44 to intersect the central bore 16.

Normal designs almost universally have allowance to drill past the angleport intersections which creates a void 54 behind the fluid flow. Such avoid is also present in the embodiment of FIGS. 1-4. This void allowsfor turbulent recirculating flow which is believed to contribute to thepotential for vortex cavitation, above that of the cavitation caused bythe adverse pressure gradient at the angled port, central boretransitions. This vortex cavitation can manifest in damage locally andfurther downstream.

For the modified flow diverter shown in FIG. 10, the closed end portion48 of the insert 14 includes closed end portions 47 of the walls 46defining the portion of the flow channels in the insert. The closed endportion 48 of the insert narrows in this embodiment to a pyramid-shapedcentral tip 56 as the portions of the flow channels 44 defined by theinsert converge.

The geometry of the insert 14 including the pyramid-shaped tip 56 isformed by simply extruding the angled flow channel along a swept path.This design effectively plugs the central bore 16 behind the fluid flowand significantly “smooths” the fluid flow as it transitions from theangled ports 44 into the central bore 16.

The pyramid-shaped tip 56 is not expected to provide a significantbenefit without the curved surfaces 20 between the central bore 16 andangled flow channels 44, as the tip 56 would likely only serve tomaintain the fluid velocity further into the angled port/central boretransition, increasing the adverse pressure gradient. The tip 56 may inthat case actually make things worse by forcing a larger volume of thefluid flow at a higher velocity closer to the 45° sharp transition.

Note that the velocity is highest in the central bore 16 exiting thepart. The flow is accelerating through the angled flow channels 44 intothe central bore 16, and we want that transition to be as smooth andgradual as possible.

Without an insert 14, a pyramidal shaped tip 56 at closed end 24 couldbe formed by simply drilling the flow channels 44 into a flow diverterthat has had the central bore drilled to a specific distance. However,that would require matching the flow channel diameters to the centralbore diameter so that the angled flow channels are drilled to intersecteach other to eliminate any remnants.

FIG. 11 is a cutaway exploded isometric view of the flow diverter andinsert of FIG. 10. The insert 14 is inserted from open end 22 of thebore 16 and comes to rest at seat 58 at the closed end 24 of the bore.

FIG. 12 is a closeup side section view of the insert 14 for the modifiedflow diverter of FIG. 10. As shown in FIG. 12, the portions of angledflow channels 44 defined by the insert 14 are curved in this embodiment.This curvature is visible in a concave profile 60 of the cross sectionof the pyramid-shaped tip 56. The curvature is modeled by “sweeping” across section of the angled flow channel through a path from the centerof the angled flow channel into the central bore at which point the“sweep” path is parallel to the central bore. This curvature is intendedto maintain an even angled flow channel cross section for as long aspossible. The curvature is believed to assist the fluid velocitytransition into the central bore resulting in a more even velocitydistribution through the transition over and above eliminating theturbulent backflow into the void 54 that is in the prior art (e.g. FIG.9) behind the angled flow channels 44.

FIG. 13 is a side section view of another prior art flow diverter. InFIGS. 13-16 the closed end connector 32 is a Constant Velocity drivejoint. FIG. 14 is a side section view of the flow diverter modified toreceive an insert as shown in FIG. 15. This version has an insertcontacting the angled flow channels 44 only at one side of theintersection with the bore 16, as in FIGS. 1-4. In addition to anexpansion 62 of the bore 16 to receive the insert, FIG. 14 also shows anoptional modification of the outer surface 18 of the housing 12 at atransition area 64 between wider and narrower portions of the housing.This modification reduces a slope of the transition area 64 to, in thisembodiment, 45 degrees instead of the steeper slope previously present.These modifications mitigate erosion on the outside of the port andcreate a flow stream with minimum recirculation and change in velocity.Some of these modification are simple but do add a significantperformance increase.

To install an insert 14, the housing 12 can be machined first and theinternal diameter recorded. The insert 14 can be formed with a slightlyhigher outer diameter, for example 0.003 inches larger. Friction pastecan be used and the housing can be heated, for example to 375° C., forexample using an induction heater, to expand the housing to allow theinsert to be installed. Alignment tools can be used to ensure the insertis properly located and the housing is allowed to cool to shrink fit. Inthe embodiment shown in FIG. 15, there is a 0.03 inch projection 68 fromthe open end portion of the insert that is trimmed flush after theshrink fit install.

FIG. 16 is another modification of the prior art flow diverter of FIG.13, this modification having a full insert as in FIGS. 6-8 and 10-12. Inaddition to the modification of the transition area 64, this one alsohas a further optional modification in that lube ports 66 are moved to acircumferential position at a 45 degree angle with respect to the angledflow channels 44 instead of being at a circumferential position matchinga flow channel.

The flow diverter embodiments disclosed here would also work for flowdiverters with flow in the opposite direction. In this case, the filletswould still prevent cavitation downstream of the change in angle of theflow, but this downstream direction would now be within the angled flowchannels 44 and not within the bore 16.

FIGS. 17 and 18 show simulations of fluid flow in flow diverters. FIG.17 shows flow in a prior art flow diverter with a sharp angle 70 betweenthe flow channel 44 and the bore 16. The shading, other than the lightshade representing solid matter or space not considered part of the flowpath, represents speed of flow, with darker being faster and lighterbeing slower. Arrows, where visible, represent direction of flow. Itshould be noted that some areas may appear darker due to the presence ofarrows. As can be seen in FIG. 17 there is an area of high flow 72 nearthe sharp angle 70 between the bore 16 and flow channel 44 and an areaof slow flow 74 downstream of the sharp angle. A recirculating flow area78 can be seen also downstream of sharp angle 70. There are 4 or 5arrows that stand out as not part of the bulk flow.

FIG. 18 shows flow in a modified diverter with a curved surface 20between the flow channel 44 and the bore 16. This simulation alsoincludes a tip 56 and the view is not as close up as in FIG. 17. As inFIG. 17, some areas may appear darker due to the presence of arrows, andthe arrows are smaller in this figure. As can be seen in FIG. 18, in themodified flow diverter the dark and light areas near the intersection ofthe bore 16 with the flow channels 44 are diminished or eliminated.

FIG. 19 shows a more full simulation view of a prior art flow diverterand omits the arrows showing flow direction. In this simulation,shading, other than pure white and the light shade, represent flow speedas in FIGS. 17 and 18, and the white areas 76, represent areas under 2psi. This is a frame of a multi-frame simulation. The areas 76 under 2psi are present in all frames and fairly consistent in size.

FIG. 20 shows a simulation of a flow diverter with curved areas 20between the bore 16 and flow channels 44, while still having a void 54.Arrows show flow direction but are too small to be easily seen. Shadesrepresent the same information as in FIG. 19, but the arrows make someareas appear darker. The areas 76 in this case show areas below 12 psi.Even with the higher threshold of 12 psi, these areas 76 are smallerthan those under the 2 psi threshold in FIG. 19 and do not show up inall frames.

FIG. 21 shows an initial frame of a simulation of a flow diverter havinga curved surface 20 and a tip 56. Shades represent the same informationas in FIG. 19. The white areas 76 quickly disappear in subsequentframes.

The areas 76 representing the volume below a pressure thresholdrepresents the “Volume fraction” (local area in the flow regime) belowthat threshold. The pressure threshold of 2 psi was estimated to be thepressure at which cavitation will form in the examples simulated. Usingthe “Volume fraction” method doesn't capture all the cavitation in theflow, only volumes or areas below the set pressure which allows us toestimate where cavitation will occur based on the liquid vapour phasetransition of water @ 60° C. Other onset forms of cavitation will alsooccur. Modeling fine areas of shear or vortex cavitation require a veryfine mesh and lots of computational horsepower. We could only find thelarge areas at this time. In the unmodified parts shown in FIG. 19 theframe shown is from a point in time in the simulation after some timehas elapsed to allow the flow to stabilize, and the areas 76 below 2 psiremain. In the modified part shown in FIG. 21 they soon disappear. Theareas 76 of pressure below 12 psi, in the frame of FIG. 20 from thesimulation for the part with curved areas 20 and void 54, are notpresent in all frames. Even in the frame shown, the area 76 is smallerthan the 2 psi area for the unmodified part as shown in FIG. 19.

Specific pressure thresholds for cavitation formation will change withdifferent conditions.

A simulation of the full insert design including closed end portion 48produced no areas in the flow below 12 psi in steady state whereas asimulation of the insert with only the curved areas 20 produced areasfrom 12 psi down to 8 psi. 8-12 psi is above the cavitation point but itpoints to an improvement in the flow regime.

In addition to the simulation results, a flow diverter with fillets 20and a tip 56 has been tested with good results.

Immaterial modifications may be made to the embodiments described herewithout departing from what is covered by the claims.

In the claims, the word “comprising” is used in its inclusive sense anddoes not exclude other elements being present. The indefinite articles“a” and “an” before a claim feature do not exclude more than one of thefeature being present. Each one of the individual features describedhere may be used in one or more embodiments and is not, by virtue onlyof being described here, to be construed as essential to all embodimentsas defined by the claims.

While the preferred embodiment of the invention has been illustrated anddescribed, as noted above, many changes can be made without departingfrom the spirit and scope of the invention. Accordingly, the scope ofthe invention is not limited by the disclosure of the preferredembodiment. Instead, the invention should be determined entirely byreference to the claims that follow.

1.-13.(canceled)
 14. A flow diverter for use in a downhole drillingmotor, the flow diverter comprising: a body defining a central borehaving an opening at a first end of the body, the body further definingflow channels angled relative to the central bore and connecting thecentral bore to an exterior surface of the body, the body definingfillets connecting the flow channels to the central bore and having aradius of curvature greater than one third of a diameter of a flowchannel of the flow channels.
 15. The flow diverter of claim 14 in whichthe radius of curvature is greater than one half of a diameter of theflow channel.
 16. The flow diverter of claim 14 in which the radius ofcurvature is greater than three quarters of a diameter of the flowchannel.
 17. The flow diverter of claim 14 in which the body comprises ahousing defining a cavity extending from the opening and an insertinserted within the cavity, the insert defining the fillets.
 18. Theflow diverter of claim 17 in which the housing is formed of a firstmaterial and the insert is formed of a second material more abrasionresistant than the first material.
 19. The flow diverter of claim 14further comprising a first connector at the first end configured toconnect the flow diverter to a bearing section of a drilling motor and asecond connector at a second end opposite to the first end configured toconnect the flow diverter to a coupling for connecting to a transmissionof the drilling motor.
 20. The flow diverter of claim 14 furthercomprising a first connector at the first end configured to connect theflow diverter to a transmission of a drilling motor and a secondconnector at a second end opposite to the first end configured toconnect the flow diverter to a coupling for connecting to a through borepower section rotor of the drilling motor.
 21. An insert for a flowdiverter for use in a downhole drilling motor, the insert defining acentral bore and having curved portions adjacent to the central boreconfigured to, when the insert is inserted in the flow diverter, formfillets connecting the central bore to flow channels defined by the flowdiverter, the flow channels being angled relative to the central boreand connecting the central bore to an exterior surface of the flowdiverter when the insert is inserted in the flow diverter.
 22. Theinsert of claim 21 further comprising inlet wall portions extendingfully around each of the flow channels. 23.-25. (canceled)